Fifty years ago this week, President Lyndon Johnson signed the Voting Rights Act, one of the most successful civil rights laws in our nation's history. The Act was designed to curb discrimination in voting and bring equality to the ballot box for all Americans, regardless of the color of one's skin. It was the culmination of more than a century of battles for black voting rights.

But two years ago, the U.S. Supreme Court, in Shelby County vs. Holder, gutted a key provision of the law. The decision came amid a new wave of laws restricting voting, the most since the Jim Crow era. The ruling destroyed a core protection that allowed the federal government, in certain places, to block discriminatory election laws before they had a chance to hurt voters.

Now, advocates are waging battles in the courts to save what is left of the Act, and calling on Congress to restore this protection to ensure voting can remain equal for all.

Our country has a long history of keeping certain people away from the ballot box. Initially, only white male landowners could vote. Black men could vote after the Civil War. For a time, many did. But soon, the Jim Crow era took hold and Southern states passed discriminatory laws and carried out a campaign of violence and intimidation aimed at preventing them from doing so. Black voter registration and political representation plummeted, and stayed that way for nearly a century.

Starting in the 1950s, the Civil Rights Movement began to make gains. Voter registration was a key goal to advance equality. One Sunday in 1965, a bloody march across the Edmund Pettus Bridge in Selma, Ala., brought dramatic attention to the cause. Americans across the country, white and black, watched as police officers beat and tear-gassed innocent people. The public outcry helped put pressure on lawmakers to pass the Voting Rights Act, which Johnson signed on Aug. 6, 1965.

The Act unleashed the potential inherent in American democracy. It was instantly effective. The gap between white and black registration rates dropped from nearly 30 percentage points in the early 1960s to just eight by the 1970s. Turnout among black voters shot up significantly. The black-white turnout gap in the South, approximately 50 percentage points in the mid-1950s, was effectively eliminated.

Over the years, as demographics have shifted, the Voting Rights Act has also expanded to include protections for Hispanics and language minorities, furthering the promise of equality for all at the ballot box.

Section 5 of the Act was particularly instrumental in achieving these remarkable successes. Under this part of the law, jurisdictions with a history of discrimination against African Americans were required to seek approval, or "preclearance," from either the Department of Justice or a federal court in Washington, D.C., for any changes to their election practices before they could put them into effect.

This was critical. It blocked and deterred discriminatory election practices — such as last-minute changes to polling locations, or consolidating districts, which could dilute minority voting strength — that earlier litigation, brought after the fact, could do little to remedy. Before 1965, when one discriminatory voting practice was blocked through litigation, defendants could turn around and adopt a slightly different restriction in its place. Section 5 aimed to bring this gamesmanship to end.

The VRA was enacted with strong bipartisan support, and Congress has reauthorized it four times. During the last reauthorization, in 2006, Congress examined thousands of pages of evidence showing that discrimination still exists and the Act was still vital. The Senate voted 98-0, and the House 390-33, to continue it for another 25 years.

Despite all this, some opponents have been skeptical of the ongoing need for these protections in the current day. And in 2013, with the support of the Supreme Court, they succeeded. The Court struck down Section 4, the formula laying out which jurisdictions had to seek federal approval for election law changes, rendering Section 5 inoperable — like a computer without an operating system.

A 5-4 majority looked at improvements in black voter registration rates and the eradication of restrictions like the poll tax to find that the "conditions that originally justified [Section 5] no longer characterize voting in the covered jurisdictions."

In her dissent, Justice Ruth Bader Ginsburg decried that the majority was holding the Act's own success against it. "Throwing out preclearance when it has worked and is continuing to work to stop discriminatory changes," she responded, "is like throwing away your umbrella in a rainstorm because you are not getting wet."

At its heart, the disagreement boils down to whether, as a nation, we still need federal protections against the possibility of racial discrimination in voting. Although we have come a long way since the 1960s, the past few years have shown that major racial divisions still exist. They may even have gotten worse since 2013, as large majorities of white and black Americans now view race relations as "generally bad," according to a recent poll.

The recent rash of discriminatory voting laws, unleashed by the Shelby County decision, does not help. States have used the court's implicit approval as justification to pass strict measures. These may not be as obviously discriminatory as literacy tests, but they similarly prevent people from voting.

For example, mere hours after the high court ruling, Texas implemented a strict photo ID law, which had previously been rejected under Section 5. That summer, the North Carolina legislature passed a sweeping law that also instituted a stringent photo ID requirement, eliminated same-day registration, and cut back on early voting.

All of these laws respond to phantom complaints of voter fraud, and all disproportionately hurt the ability of minorities to vote. In October 2014, a federal judge found 600,000 registered Texas voters do not have acceptable ID. Testimony showed African-American and Hispanic registered voters are two to four times more likely than white registered voters to lack photo ID. In North Carolina, data showed African Americans used early voting and same-day registration at much higher rates than whites.

Overall, since the 2010 election, 21 states have imposed new voting restrictions. In 2016, 15 states will have more strict rules than they did in 2012. The storm of discriminatory changes forecast by Ginsburg has apparently come to pass.

Many of these measures have been aggressively challenged under the remaining sections of the Voting Rights Act. Two major cases are pending in Texas and North Carolina, where attorneys laid out strong evidence showing how these laws prevent citizens from voting, and disproportionately discriminate against blacks and Hispanics.

Take Sammie Louise Bates, a witness in the Texas trial in September 2014. As the only one in her family who attended school, in a small town in Mississippi, Bates helped her grandmother count out her poll tax, a fee imposed with the intent to discourage black voters from voting

This made her angry — and inspired her to become a lifelong voter. But in 2013, Texas's new photo ID law prevented her from casting a ballot. She had her voter registration card, containing her name and current address, and an Illinois photo ID — both of which would have been sufficient to prove her identity in prior elections. But when she tried to get a Texas ID, she kept running into the same obstacle: She needed to obtain her Mississippi birth certificate, which would cost $42.

"I had to put $42 where it was doing the most good," she stated. "It was feeding my family, because we couldn't eat the birth certificate. That's for sure. And we couldn't pay rent with the birth certificate."

Bates was one of approximately 16 witnesses who testified about the difficulties they personally faced in obtaining acceptable ID, ranging from insufficient funds to endless red tape. After hearing multiple expert analyses, Judge Nelva Gonzales Ramos struck down the law in October 2014 as discriminatory under Section 2 of the Voting Rights Act.

Yet, despite this evidence, the Supreme Court allowed it to remain in effect for the November 2014 election, pending an appeal that has still not been resolved.

This highlights the single most important loss in the Supreme Court's Shelby County decision. Before, voting laws could not go into effect in certain jurisdictions until the state had demonstrated they did not discriminate. After the ruling, laws must be challenged in case-by-case litigation that is costly and can take years. As a result, those measures can remain on the books to disenfranchise voters like Bates. And there's no guarantee that a victory won't simply give way to additional restrictions.

Another major lawsuit is also pending in North Carolina, where a trial just wrapped up. Its laws are also being challenged under the remaining provisions of the Voting Rights Act and the Constitution. At least one of these cases is likely to make it to the Supreme Court. What the court decides will determine not just the fate of those laws, but what is left of the Voting Rights Act.

Despite these fights, several states have advanced bipartisan reforms to modernize voter registration in recent years. They seek to streamline the process and increase access for all voters. Oregon, for example, passed a law to automatically sign up eligible citizens in the motor vehicle database. Hillary Clinton recently embraced a form of automatic and universal registration. Rand Paul supports restoring voting rights to some people with past convictions. Other states have expanded early voting opportunities and moved registration online.

But while all leaders should work to create a voting system that works well for everyone, they must also fight for one that discriminates against no one.

We have been painfully and repeatedly reminded in recent days and months about the continuing necessity of working for racial justice and equality in America. The Voting Rights Act, which gets at the core of democracy, is essential to the fight.

At the 50th anniversary of the March from Selma to Montgomery earlier this year, civil rights leaders convening in Alabama were united around this common purpose. This time, however, instead of seeking passage of the Voting Rights Act, they sought its restoration.

Whatever one's views of the Shelby County decision, and however one feels about the Court's view that "our country has changed," there is no question the Supreme Court believes Congress has the power to act. It practically invited action by acknowledging that "while any racial discrimination in voting is too much, Congress must ensure that the legislation it passes to remedy that problem speaks to current conditions."

Today, Congress has introduced two separate bills — the Voting Rights Amendment Act and the Voting Rights Advancement Act — that would restore the lost protections of Section 5, making it operative once again, and modernize the Voting Rights Act for the 21st century. On this historic anniversary for our country, Congress should move swiftly to restore the lost promise of the Voting Rights Act.

Theodore M. Shaw is the Julius L. Chambers Distinguished Professor of Law and the Director of the Center for Civil Rights at the University of North Carolina at Chapel Hill School of Law. He served as director-counsel and president of the NAACP Legal Defense Fund from 2004 to 2008.